The present invention relates to a device for controlling the turn-on of an eraser of a copier and, more particularly, to an eraser turn-on control device for a copier of the type which erases before developing a needless charge deposited in the area of a photoconductive element other than an image area.
In a copier of the type described, it has been customary to prevent edges (lines) of an original document from being reproduced by turning on an eraser as far as those positions which are slightly inwardly of the edges of the document. On the other hand, there is an increasing demand for a capability of copying the entire surface of an original document without leaving any blank on a copy. Such full-surface copying is implemented by limiting the turn-on range of an eraser to 2 to 3 millimeters outside of the edges of a document. A problem with this kind of scheme is that even the outside of a document size is imaged on a photoconductive element and, in addition, it is located outside of a transfer region. This is not a problem so long as a cover plate is closed because the underside of the cover plate (which is usually colored in white or substantially white) is imaged. However, when the cover plate is open, light issuing from an illuminating unit fails to be reflected and therefore forms a black portion on a photoconductive element, resulting in wasteful consumption of toner. Further, since such a black portion is moved to a cleaning unit without being transferred to a paper, the cleaning unit has to be provided with a considerable cleaning ability. When toner remaining on the photoconductive element after image transfer is not completely removed, it appears on the subsequent copies as a smear.